# Equivalence Principle: Einstein vs Strong

• Andre' Quanta
The Einstein equivalence principle states that the laws of physics are the same for all observers in uniform motion in a given reference frame. This can be formulated as a chart or reference frame in which the metric is Minkowski and its first derivative is null at every point in space-time. The strong equivalence principle, on the other hand, extends this to include non-uniformly accelerating observers and states that the laws of physics are the same for all observers in any reference frame, regardless of acceleration. In summary, the Einstein equivalence principle and the strong equivalence principle both state that the laws of physics are the same for all observers, but the strong equivalence principle includes non-uniform acceleration.
Andre' Quanta
1-What is the different between the Einstein equivalence principle and the Strong equivalence principle?
2-Is it possible to formulate the Einstein equivalence principle in this way?
"For every point in space time, always exist a chart / reference frame in which the metric in that point is Minkowski and its first derivative is null"

Another good reference is Clifford Will's "The Confrontation between General Relativity and Experiment" http://relativity.livingreviews.org/Articles/lrr-2014-4/fulltext.html . The Einstein equivalence principle is given in section 2.1, and the strong equivalence principle is given in section 3.1.

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This is nice too!

Andre' Quanta said:
2-Is it possible to formulate the Einstein equivalence principle in this way?
"For every point in space time, always exist a chart / reference frame in which the metric in that point is Minkowski and its first derivative is null"

Yes.

## What is the Equivalence Principle?

The Equivalence Principle is a fundamental concept in physics that states that the effects of gravity and acceleration are indistinguishable. In other words, an observer in a gravitational field will experience the same physical phenomena as an observer in an accelerated reference frame.

## How did Einstein's theory of General Relativity challenge the Equivalence Principle?

Einstein's theory of General Relativity proposed a new understanding of gravity as the curvature of spacetime caused by the presence of mass and energy. This challenged the traditional interpretation of gravity as a force, which was based on Newton's theory of gravity. According to General Relativity, the Equivalence Principle applies not just to uniform acceleration, but to any gravitational field.

## What is the difference between Einstein's Equivalence Principle and the Strong Equivalence Principle?

Einstein's Equivalence Principle, also known as the Weak Equivalence Principle, states that the effects of gravity and acceleration are equivalent only for small regions of spacetime. The Strong Equivalence Principle, on the other hand, extends this principle to apply to all physical laws, not just the laws of mechanics. This means that the Strong Equivalence Principle includes the effects of gravity on electromagnetism and other forces.

## What evidence supports the Equivalence Principle?

One of the strongest pieces of evidence for the Equivalence Principle is the phenomenon of gravitational time dilation. This occurs when clocks in a stronger gravitational field are observed to run slower than clocks in a weaker gravitational field. This effect has been confirmed through experiments and observations, including the famous Pound-Rebka experiment in 1959.

## How does the Equivalence Principle impact our understanding of the universe?

The Equivalence Principle is a crucial concept for understanding gravity and its effects on the universe. It has been used to make predictions and explain phenomena such as the bending of light by massive objects, the behavior of black holes, and the expansion of the universe. It also plays a key role in the development of theories such as General Relativity and quantum gravity.

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